<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<script src="jquery/1.10.2/jquery.min.js">
	
</script>
<script>
	$(document).ready(function() {
		$("button").click(function() {
			$("#div1").addClass("important blue");
		});
	});
</script>
<style type="text/css">
.important {
	font-weight: bold;
	font-size: xx-large;
}

.blue {
	color: blue;
}
</style>
</head>
<body>

	<div id="div1">这是一些文本。</div>
	<div id="div2">这是一些文本。</div>
	<br>
	<button>为第一个 div 元素添加类</button>

</body>
</html>